1. Field of the Invention
The present invention relates to a technique of automatically controlling a clutch provided in a vehicle.
2. Description of the Related Art
A vehicle provided with a transmission device can perform a shift change by changing a transmission gear ratio in the transmission device. In order to perform a shift change, a clutch provided upstream of the transmission device must be disengaged so that torque from the engine is not transmitted to the transmission device.
One type of transmission device is a manual transmission device in which the operation of engaging and disengaging the clutch is manually controlled by a driver. Another type of transmission device is an automatic transmission device in which the operation of engaging and disengaging the clutch is controlled automatically.
A person driving a vehicle provided with a manual transmission device adjusts an engine speed, a vehicle acceleration, and time until the clutch engages by operating the accelerator and clutch at the time of starting the vehicle. The driver attempts to start the vehicle as he/she intends by operating the accelerator and the clutch. In other words, the driver might feel uncomfortable about abrupt acceleration and stressful about too slow acceleration. The driver performs the accelerator operation and the clutch operation so that acceleration is as smooth and comfortable as possible. In the moment that the clutch starts to engage in particular, in other words, the moment the clutch starts to transmit torque, a slight shock may occur. The driver can reduce the magnitude of the shock by carefully carrying out the engagement operation of the clutch.
As for a vehicle provided with an automatic transmission device, it is desirable that traveling proceeds as intended by a driver at the time of starting the vehicle. In addition, the shock that may occur at the moment the clutch is engaged is preferably as small as possible.
JP 61-38229 U discloses a technique using an automatic clutch device. The disclosed automatic clutch device is adapted to select among preset different clutch control patterns in response to a change ratio for an accelerator position. More specifically, a control pattern for a sudden start and climbing start is selected if the accelerator position corresponds to a prescribed value or more, and a control pattern for a normal start is selected if the position corresponds to a value less than the prescribed value so that the clutch control based on the control patterns is performed.
JP 2008-232421 A discloses a clutch controller. The clutch controller is controlled such that, if the engine is operated in a predetermined driving range, torque transmitted to the downstream side through the clutch is approximated to the engine torque.